Gas-liquid reactions occur frequently in chemical process technology. Examples are oxidations, hydrogenations, chlorinations or biochemical reactions with consumption of oxygen. These reactions are in many cases also carried out with the addition of a solid component, e.g. a catalyst.
There are numerous proposals for reactors for carrying out such reactions, which often envisage a gassing stirrer for mixing in the gaseous reactants. Thus, for example, M. Zlokarnik, Rührtechnik, p. 174 et seq., Springer Verlag, 1999 or EKATO Handbook of Mixing Technology, p. HY.1 et seq., Ekato Rühr-und Mischtechnik GmbH, Schopfheim, Germany describe gassing stirrers.
EP 784 505 A describes a slurry phase reactor for exothermic reactions, in particular for the hydrogenation of aromatic nitro compounds, having a stirrer for circulating the reaction mixture and an additional gassing stirrer. The reaction partners are led into the reactor via a metering tube in the immediate vicinity of the stirrer which is employed for circulating the reaction mixture. Depending on the conveying direction and conveying characteristics, the reactant is deflected in the radial or axial direction and thereby mixed into the volume stream sucked in by the stirrer.
U.S. Pat. No. 3,761,521 discloses a process and a device for carrying out continuous reactions, e.g. the hydrogenation of aromatic nitro compounds. In this, a reaction mixture is formed by mixing a gaseous phase and a second solid or liquid phase in a liquid medium. During the mixing, the gas is dispersed rapidly in the liquid phase. Some of the liquid phase overflows continuously from the stirred reaction space into a separator for the catalyst. The gas and the liquid phase are fed to the stirrer via tubes from the top, the stirrer sucking in further gas via a hollow shaft.
M. Assirelli, W. Bujalski, A. W. Nienow, A. Eaglesham, “Intensifying Micromixing with a Rushton Turbine”, 5th International Symposium on Mixing in Industrial Processes, Sevilla, Spain, 2004 describes a reaction in a stirred reactor in which one of the reactants of the reaction mixture is fed in close to the stirrer. The feeding in of the one reactant takes place here via a hollow shaft, from which three curved tubes branch off. The tubes end at some distance from the edges of the stirrer blades in the vertical and horizontal direction. The radially conveying disc stirrer described has six blades. Moreover, the use of a gassing stirrer is not described herein.
In gas-liquid reactions, gassing stirrers which are connected to the gas space above the level of the liquid via a hollow shaft are also employed to intensify the gassing. The gassing stirrers are particularly suitable for redispersing the not yet completely reacted gaseous reaction partner. M. Zlokarnik, H. Judat, “Rohr-und Scheibenrührer-Zwei leistungsf{dot over (a)}hige Rührer zur Flüssigkeitsbegasung”, Chemie-Ingenieur-Technik 39, volume 20, p. 1163-1168, 1967 describes a stirrer which is constructed as a four-armed tubular stirrer. Two opposite arms suck in gas and the other two arms liquid. The conveying capacity of the liquid stirrer drops sharply when the gas trail reaches and envelops the next arm.
BE 869 961 A describes a stirrer in the form of a disc, wherein the stirrer is equipped with various nozzles for gas and liquid. The gas or liquid is introduced under pressure via the nozzles, so that in the event of failure of the stirrer motor settling of the suspension can be avoided for a certain period of time. This device is not suitable for independent conveying or for metering in during normal stirrer operation.
The difficulty in reactors for gas-liquid reactions, in addition to a good distribution of the gas phase, lies in mixing the liquid reactants into the reaction mixture as uniformly as possibly, since any local excess concentration can lead to the formation of by-products, and in the case of catalysis by solids also to deactivation of the catalyst due to a local overload. Optimizing the mixing in both of the gas and of the liquid without the gas and liquid interfering with one another is a further object. For example, in the case of the four-armed tubular stirrer, which is known e.g. from M. Zlokarnik, H. Judat, “Rohr- und Scheibenrührer-Zwei leistungsf{dot over (a)}hige Rührer zur Flüssigkeitsbegasung”, Chemie-Ingenieur-Technik 39, volume 20, p. 1163-1168, 1967, a drop in the conveying capacity of the liquid stirrer occurs due to the formation of the gas trail. This drop in capacity also has an adverse effect on the mixing.